Re: SCSI vs SATA

In summary, it seems one of these is true:

1. Drive manufacturers don't design server drives to be more
reliable than consumer drive

2. Drive manufacturers _do_ design server drives to be more
reliable than consumer drive, but the design doesn't yield significantly
better reliability.

3. Server drives are significantly more reliable than consumer
drives.

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Scott Marlowe wrote:
> On Thu, 2007-04-05 at 23:37, Greg Smith wrote:
> > On Thu, 5 Apr 2007, Scott Marlowe wrote:
> >
> > > On Thu, 2007-04-05 at 14:30, James Mansion wrote:
> > >> Can you cite any statistical evidence for this?
> > > Logic?
> >
> > OK, everyone who hasn't already needs to read the Google and CMU papers.
> > I'll even provide links for you:
> >
> > http://www.cs.cmu.edu/~bianca/fast07.pdf
> > http://labs.google.com/papers/disk_failures.pdf
> >
> > There are several things their data suggests that are completely at odds
> > with the lore suggested by traditional logic-based thinking in this area.
> > Section 3.4 of Google's paper basically disproves that "mechanical devices
> > have decreasing MTBF when run in hotter environments" applies to hard
> > drives in the normal range they're operated in.
>
> On the google:
>
> The google study ONLY looked at consumer grade drives. It did not
> compare them to server class drives.
>
> This is only true when the temperature is fairly low. Note that the
> drive temperatures in the google study are <=55C. If the drive temp is
> below 55C, then the environment, by extension, must be lower than that
> by some fair bit, likely 10-15C, since the drive is a heat source, and
> the environment the heat sink. So, the environment here is likely in
> the 35C range.
>
> Most server drives are rated for 55-60C environmental temperature
> operation, which means the drive would be even hotter.
>
> As for the CMU study:
>
> It didn't expressly compare server to consumer grade hard drives.
> Remember, there are server class SATA drives, and there were (once upon
> a time) consumer class SCSI drives. If they had separated out the
> drives by server / consumer grade I think the study would have been more
> interesting. But we just don't know from that study.
>
> Personal Experience:
>
> In my last job we had three very large storage arrays (big black
> refrigerator looking boxes, you know the kind.) Each one had somewhere
> in the range of 150 or so drives in it. The first two we purchased were
> based on 9Gig server class SCSI drives. The third, and newer one, was
> based on commodity IDE drives. I'm not sure of the size, but I believe
> they were somewhere around 20Gigs or so. So, this was 5 or so years
> ago, not recently.
>
> We had a cooling failure in our hosting center, and the internal
> temperature of the data center rose to about 110F to 120F (43C to 48C).
> We ran at that temperature for about 12 hours, before we got a
> refrigerator on a flatbed brought in (btw, I highly recommend Aggreko if
> you need large scale portable air conditioners or generators) to cool
> things down.
>
> In the months that followed the drives in the IDE based storage array
> failed by the dozens. We eventually replaced ALL the drives in that
> storage array because of the failure rate. The SCSI based arrays had a
> few extra drives fail than usual, but nothing too shocking.
>
> Now, maybe now Seagate et. al. are making their consumer grade drives
> from yesterday's server grade technology, but 5 or 6 years ago that was
> not the case from what I saw.
>
> > Your comments about
> > server hard drives being rated to higher temperatures is helpful, but
> > conclusions drawn from just thinking about something I don't trust when
> > they conflict with statistics to the contrary.
>
> Actually, as I looked up some more data on this, I found it interesting
> that 5 to 10 years ago, consumer grade drives were rated for 35C
> environments, while today consumer grade drives seem to be rated to 55C
> or 60C. Same as server drives were 5 to 10 years ago. I do think that
> server grade drive tech has been migrating into the consumer realm over
> time. I can imagine that today's high performance game / home systems
> with their heat generating video cards and tendency towards RAID1 /
> RAID0 drive setups are pushing the drive manufacturers to improve
> reliability of consumer disk drives.
>
> > The main thing I wish they'd published is breaking some of the statistics
> > down by drive manufacturer. For example, they suggest a significant
> > number of drive failures were not predicted by SMART. I've seen plenty of
> > drives where the SMART reporting was spotty at best (yes, I'm talking
> > about you, Maxtor) and wouldn't be surprised that they were quiet right up
> > to their bitter (and frequent) end. I'm not sure how that factor may have
> > skewed this particular bit of data.
>
> I too have pretty much given up on Maxtor drives and things like SMART
> or sleep mode, or just plain working properly.
>
> In recent months, we had an AC unit fail here at work, and we have two
> drive manufacturers for our servers. Manufacturer F and S. The drives
> from F failed at a much higher rate, and developed lots and lots of bad
> sectors, the drives from manufacturer S, OTOH, have not had an increased
> failure rate. While both manufacturers claim that their drives can
> survive in an environment of 55/60C, I'm pretty sure one of them was
> lying. We are silently replacing the failed drives with drives from
> manufacturer S.
>
> Based on experience I think that on average server drives are more
> reliable than consumer grade drives, and can take more punishment. But,
> the variables of manufacturer, model, and the batch often make even more
> difference than grade.
>
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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
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